this is a very interesting read I found... I will copy paste:

It seems that car thieves have found another way to steal your car or
truck without any effort at all. The car thieves peer through the windshield of your car or truck, write down the VIN number from the label on the dash, go to the local car dealership and request a duplicate key based on the VIN number.

The car dealer's parts dept will make a duplicate key from the VIN
number and collect payment from the thief who will return to your car. He doesn't have to break in, do any damage to the vehicle, or draw attention to himself. All he has to do is to walk up to your car, insert the key and off he goes to a local chop shop with your vehicle. You don't believe it? It IS that easy.

To avoid this from happening to you, simply put some tape (electrical tape, duct tape or medical tape) across the VIN label located on the dash ! board. By law, you cannot remove the VIN number, but you can cover it so it can't be viewed through the windshield by a car thief.


-Mike

 

Actually, dealers are SUPPOSED to ask for a registration and a photo ID to make sure you own the vehicle.

Another thing I have read and seen is if you take it to a shop and a thief works there they will make a copy of the key or write down the VIN, etc..

I have had one of my vehicles stolen once and this is what happened to me..

Another easy way to prevent this is to change the lock cylinders..